This invention relates to novel, emulsion copolymers having siloxane crosslinking functionality and more particularly to a concurrent free radical and cationic initiated aqueous emulsion polymerization process for preparing the copolymers. The copolymers are formed from at least one free radical polymerizable monomer, at least one monomer which yields a linear polysiloxane under aqueous cationic polymerization conditions ("linear siloxane precursor") and at least one monomer containing both a free radical polymerizable functionality and a silicon functionality capable of crosslinking by a siloxane condensation reaction.
As used herein "silane" shall include monomers capable of being formed into polymers having the structural formula EQU (R.sub.n SiO.sub.((4-n)/2)).sub.x
where R may be at least one of hydrogen, alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, alkaryl, or aralkyl hydrocarbons, halogen and cyano derivatives of such hydrocarbons, and hydrocarbons containing ether, thioether, ester or thioester linkages, such as for example, methyl, ethyl, propyl, butyl, amyl, dodecyl, octadecyl, myricyl, vinyl, allyl, hexenyl, ethynyl, propargyl, cyclobutyl, cyclohexyl, cyclohexenyl, phenyl, naphthyl, xenyl, tolyl, xylyl, mesityl, t-butylphenyl, benzyl, 2-phenylethyl, 2-phenylpropyl, 2-chloropropyl, 3,3,3-trifluoropropyl, chlorocyclohexyl, bromophenyl, dicychlorophenyl, alphaalphaalpha-trifluorotolyl, mercapoethyl, mercaptopropyl, mercaptodecyl, cyanoethyl, cyanopropyl, hydroxypropyl, and the like as set forth in U.S. Pat. No. 3,575,910, referred to hereinafter; and where n has an average value of from 0.5 to less than 3, and where x is at least 2 or greater and is typically several hundred or greater. The disclosure will also refer to the nomenclature in the silicone art commonly used to identify the four basic types of alkoxy silanes or siloxane structural units: M,D,T and Q. These designations refer to the number, of Si-O bonds in the smallest repeating unit, (from 1 to 4) with, for example, Q refering to (4) silicate.
The incorporation of siloxane functionality into polymers is desirable for improving a variety of physical or chemical properties such as for example: improved weatherability as by increasing resistance to ultraviolet radiation, oxygen, water or solvents; thermal stability; or to improve or facilitate adhesion or bonding to selected substrates.